The invention relates to an improvement in the distillation of crude oil.
Briefly, the distillation of crude oil is normally carried out in multiple stage fractional distillation columns having a number of side raw product streams. In such columns, the liquid is vaporized or flashed in a lower flash zone, and flash vapor is fractionated in the upper portion of the column. The section of trays between the flash zone and the lowest sidedraw is called the de-entrainment section. The primary function of the de-entrainment section is to remove drops of liquid entrained in the vapor leaving the flash zone. Liquid from the bottom tray of the de-entrainment section, the distillate portion of which is sometimes called overflash, is either drained to the flash zone or recycled back to the crude heater.
The process designer is faced with two conflicting design requirements for the de-entrainment section. First, there must be sufficient reflux liquid on the trays to obtain effective contacting of liquid and vapor, and consequent removal of black oil drops entrained from the flash zone, and, second, for maximum distillate yield and thermal efficiency, overflash should be as low as possible. In the typical design, a compromise must be made between these two requirements. Accordingly, a need has existed for an improved process for distillation of crude oil which overcomes these limitations. The invention is such a process.